Charmonium - In and out of the nucleus

The bound states of charm and anticharm quarks, charmonium, offer a unique opportunity to explore the relationship between the traditional way of understanding hadronic interactions in nuclear physics, i.e., in terms of meson exchanges, and the QCD based description in terms of gluon exchanges. Inserting charmonium, for example J/ψ, into the nucleus leads to many interesting possibilities. Several of these are mentioned. One, namely J/ψ attenuation in nuclei, is discussed in some detail because of its importance as the possible signature of quark-gluon plasma(QGP) formation in relativistic heavy ion collisions. A technique for the direct measurement of J/ψ -nucleon cross section is proposed.